This might be extraordinarily simple, but I am playing with Emacs (22.1.1) and I can\'t get it to paste text in the clipboard using Control-Y.
Try using the M-x clipboard-yank command. If you want to copy text to the clipboard you have to M-x clipboard-kill-region.
M-x clipboard-yank
M-x clipboard-kill-region
This works on Linux and Windows, I guess on Mac it's the same.